Although there exists a variety of tests currently used to assess pancreatic exocrine function none have the combined features of reliability, ease of performance or are rapid in yielding results. The principles and problems of breath tests are discussed in a paper by Lo and co-authors in Advances in Pediatrics, Vol. 29, pp. 105-127 (1982).
Tests to ascertain pancreatic exocrine function are generally categorized as direct or indirect. Direct tests as described by Lankisch in GUT, Volume 23, pp. 777-798 (1982), involve measuring biochemical parameters, most often enzymes, secreted in duodenal juice after exogenous hormonal stimulation of the pancreas. The major technical problem associated with Direct tests is that duodenal intubation by professional personnel is required; the procedure is expensive and uncomfortable to the patient. In addition, the location of the tube must be confirmed by fluoroscopy, and when such is done, the patient receives radiation exposure. In addition, the patient has the discomfort (and possible major side effects) caused by the intravenous administration of a hormone. Finally, there is the problem of incomplete recovery of duodenal secretions, which to be properly corrected for, requires the additional use of a recovery marker.
Indirect tests are distinguishable from Direct tests in that they make use of nutrients, generally a meal fed to the patient, in lieu of exogeneously administered hormones, to stimulate pancreatic function. Indirect tests are subdivided into two classes, those that require duodenal intubation, and those that do not. The disadvantages of Indirect tests that utilize intubation methods are similar to those associated with Direct tests. That is, the act of collecting duodenal juice is technically demanding, painful, involves radiation exposure and is subject to quantitative uncertainties. Indirect tests that do not require intubation are not subject to the technical difficulties of duodenal fluid collection, or intubation. These tests generally require that a patient ingest a meal to stimulate pancreatic function with an enzymatic substrate that is acted on by pancreatic enzymes in the duodenum. The substrate is hydrolyzed and the products are absorbed from the intestine, enter the blood stream and may subsequently be excreted. They may be measured in blood, urine, stool or breath. The prior art shows the existence of several Indirect tests. One of these, as described by Kimura and coworkers in Digestion, Vol. 21, pp. 133-139 ( 1981), is based on the hydrolysis of an amino acid derivative, N-benzoyl-L-tyrosyl-p-aminobenzoic acid (NBT-PABA), by the pancreatic enzyme chymotrypsin in the duodenum. Hydrolysis by chymotrypsin causes the release of p-aminobenzoic acid which is measured in serial blood samples or in the urine after a six to nine hour collection period. A second test as described by Kaffornick and coworkers in Munch. Med. Wochenschr, Vol. 119, pp. 1467-1470 (1977), involves the ingestion of fluorescein dilaurate with a meal followed by measuring the amount of fluorescein released by pancreatic esterase. The fluorescein may be measured in serial blood samples. Alternatively, urine is collected for ten hours before being analyzed for fluorescein content. The reliability of both of these tests is subject to interfering chemicals in the urine, and the urinary excretion of both products (PABA and fluorescein) may not be complete.
There have been several previous unsuccessful attempts to establish breath tests to assess pancreatic function. Both are premised on measuring the amount of .sup.14 CO.sub.2 expired in the breath that is derived from labelled fatty acid, which has been liberated by pancreatic lipase hydrolysis of either triglyceride or trioleoylglycerol esters followed by subsequent absorbtion and oxidation in the body of the radioactive fatty acid. For several reasons, however, neither test has proved useful. Utilization of triglycerides as described by Ghoos and coworkers in Digestion, Vol 22, pp. 239-249 (1981), as a substrate for pancreatic esterases where a radioactive fatty acid occupies the two position of the molecule prevents rapid liberation of the fatty acid since the two position of the triglyceride is not cleaved by pancreatic esterases. Accordingly, the fatty acid can only be cleaved after it isomerizes to the one position, a process that could be rate limiting in the oxidation of the radioactive fatty acid, and hence lead to incorrect conclusions concerning pancreatic exocrine function. Alternatively, the two ester might be absorbed in the body intact and subsequently hydrolyzed by enterocyte enzymes, in which case hydrolysis of the molecule would not be an accurate indication of pancreatic exocrine function. Similarly, King and coworkers have shown in Gastroenterology, Vol. 84, pp. 1208 (1983) that the use of trioleoylglycerol, commonly known as triolein, containing radioactive oleic acid as a substrate for pancreatic esterases is not reliable since oleic acid is absorbed more slowly by the intestinal mucosa, and, moreover is reesterified in the enterocyle and only slowly and incompletely oxidized to .sup.14 CO.sub.2.
It is apparent that both the Direct and Indirect tests currently used to assess pancreatic exocrine function have several shortcomings. Specifically, these tests variously require intubation, multiple blood samples or lengthy collection of urine or breath samples [6-10 hours], are subject to interfering chemicals, and may not be specific indicators of pancreatic function.